The rapid development of the xe2x80x9cnew economyxe2x80x9d in recent years has required office workers at all levels to spend ever-increasing amounts of time working at computers. No longer is the use of a keyboard the province of a typist/secretary or word processor operator. Managers frequently communicate by E-mail and access company data and websites for information required for carrying out their duties. Product design and development, purchasing, marketing, production, shipping, and virtually all other activities in industry and commerce are done with the aid of computers. Professionals likewise use computers for obtaining information, communicating, and for creating documents and computer data files.
Sitting upright in a somewhat forward-leaning position to work at a keyboard places considerable strain on the back and is highly fatiguing. Minimizing strain and fatigue requires a chair that provides excellent support for the user""s back, not only in a working position but a relaxed position. In that regard, it is also important for reducing strain for persons working at a computer or over papers on a desk to be able to change their positions frequently and to be able to lean back to a rest position from time to time.
Currently available office chairs allow various adjustments that improve seating comfort in working and relaxed postures. For example, seat mounts that allow the entire chair to tilt backward and forward are very common. Some office chairs have back supports that tilt backward relative to the seat bottom or seat bottoms that slide forward and backward relative to the back support, or both. Most typists chairs have a back support that pivots so as to self-adjust to the sitting posture of the user. Office chairs usually have a support column that permits adjustment of the height of the entire seat (bottom and backrest) above the floor. Many typists chairs also provide for adjustment of the height of the back support relative to the seat.
A need that has not, to the present inventor""s knowledge, been adequately met by previously known and/or available office chairs is a chair back that provides good support for the entire anatomical back of a user from the sacrum to the shoulders over a range of seating postures. On the one hand, office chairs designed for use by typists have a back support that self-adjusts about a horizontal pivot axis but is relatively small so that it supports only the lower back. Managerial and executive chairs, on the other hand, have large back supports that are of fixed shapes. The anatomical back assumes widely different vertical curvatures, depending on the seating posture. Chair back supports of fixed shapes provide good support in only one seating posture.
One object of the present invention is to provide an office chair that provides optimal support of the entire back of a user in a wide range of sitting postures. Another object is to provide an office chair of relatively simple construction that permits adjustments of the configurations of the back support and the seat bottom to suit ideally users of all heights. It is also desired to make a chair that meets the foregoing objects attractive in appearance.
The foregoing objects are attained, in accordance with the present invention, by a chair that has a pair of spaced-apart back support mounting members, a lower back support adapted to support the lower portion of the back of a person seated on the chair and mounted on the back support mounting members for pivotal movement about a pivot axis located at substantially the vertical centerline of the lower back support, and an upper back support adapted to support the upper portion of the back of a person seated on the chair and mounted on the back support mounting members for pivotal movement about a pivot axis located at substantially the vertical centerline of the upper back support.
The two back support members of the chair of the present invention provide support of a user""s back throughout the region from the sacrum to just above the shoulder blades, which relieves strain on the user""s back in all sitting postures and also considerably improves the comfort of the chair in all sitting postures, especially in a leaning back posture. The pivoting of the two back supports independently permits each back support to self-adjust to the curvature in the vertical direction of the user""s back, which varies considerably over a range of sitting postures. Pressure loads transferred from back supports to the user""s back are, by virtue of the pivoting of both back supports, relatively evenly distributed over the user""s back.
The lower back support and upper back support are, preferably, mounted on the back support mounting members by resilient mount units that bias the back supports to a predetermined position. The principal function of the resilient mounting of the two back supports is to keep both back supports in a neutral position when the chair is unoccupied so that it looks better and also so that when someone first sits down, the back supports are in proper position to encounter the user""s back with relatively even pressure rather than being far out of position and presenting edges of the supports to the user""s back. The spring force acting on each back support should, however, be kept low so that there is little effect on the pressure applied to the user""s back when the back supports pivot against the resilient biasxe2x80x94i.e., so that a substantially uniform pressure is applied by each back support to the portion of the user""s back engaged by the back support.
Each of the resilient mount units may include an elastomeric body affixed to and interposed functionally between the back support and the back support mounting member. Resilient mount units based on elastomeric members, which are known per se and are commercially available, are quiet in operation, relatively inexpensive, small and compact in size, and easy to install. Various mechanical spring systems can also be used.
In preferred embodiments, the back support mounting members are located laterally abreast of the back supports. That relative disposition of the back supports and the back support mounting members has structural and manufacturing advantages. For example, the back supports may be made large in size, both in height and width; by supporting each of them at each side edge at a single pivot point, torsion loads at the mounting points are not a factor in the design. Each back support, preferably, includes a structural pan for maintaining the shape of the back support under load and for transmitting loads laterally outwardly to the back support mounting members and upholstered padding carried by the pan.
Each of the back supports is, in preferred embodiments, generally rectangular, and the side edges of each of the back supports are closely adjacent the back support mounting members. That configuration provides wide back supports, which distribute the loads applied to the user""s back over a large area transversely and for any given total load reduce the pressure on the user""s back. Similarly, the upper edge of the lower back support is closely adjacent the lower edge of the upper back support. In addition to keeping the back supports large in area for reduced pressure, the lack of a gap between the two back supports improves the comfort by maintaining continuity of support in the vertical direction.
It is desirable that each of the lower back support and the upper back support be transversely curved and present a transversely concave front surface that corresponds in shape generally to the transverse curvature of the anatomical back of a person. Also, the lower back support is vertically curved and presents a vertically curved convex surface that corresponds in shape generally to the vertical curvature of the lower portion of the anatomical back of a person in the region of the small of the back at the waist.
The chair back structure described above is, of course, mounted on a base having a seat mount supporting a seat bottom. The chair back structure is, preferably, mounted on a back support bracket associated with the seat mount. The back support mounting members are, in preferred embodiments, joined by a transverse framework that is supported by the back support bracket for adjustment of the height of the back support mounting members.
According to another aspect of the present invention, a chair according to the present invention has a seat bottom unit having a body part and a front edge part, the rear edge of the front edge part being coupled to the front edge of the body part for downward articulation of the front edge part from a resiliently restrained upward position. The downwardly tilting front part of the seat bottom allows the front part of the seat to tilt down in response to pressure from the undersides of the lower parts of the user""s thighs, thus relieving pressure on them. The seat bottom should be mounted on the seat mount for adjustment forwardly and rearwardly relative to the seat mount so that the chair can be adjusted to suit ideally the height of the user.
In a particularly advantageous construction of the resilient mount units, a first support plate is affixed to one side of the elastomeric member and to the structural pan. A second support plate is affixed to the other side of the elastomeric member. A mounting bracket is affixed to the back support mounting member, and a screw affixes the mounting bracket to the second support plate. The structural pan includes a cavity receiving the first support plate and a portion of the elastomeric member. Each back support mounting member is a tubular member having side walls, and the mounting bracket includes a mounting post that passes through a hole in one side wall of the back support mounting members and is joined to the opposite side wall of the back support mounting members by a weldment at a weld site that includes a hole in the opposite side wall. One advantage of the foregoing construction is that the mounting bracket is very strongly joined to the back support mounting member by passing through a hole in one wall and being joined to the opposite wall by welding at a weld site formed by a hole in the opposite wall. The hole and the weld form two attachment points for the mounting post to the back support mounting member. If desirable or necessary for torsional strength about the pivot axis, both support points can be welded. Another advantage is that the resilient mount can be virtually completely concealed for good appearance of the chair. Furthermore, assembly of each back support to the back support mounting members is facilitated by having a single screw for attaching the bracket of the resilient mount unit.